Some of the sensor modules of pressure sensors include a diaphragm, four strain gauges for detecting a strain, and resistor element connectors and electrodes connected to the strain gauges, the strain gauges, the resistor element connectors and the electrodes being provided on the diaphragm, where a part of each of the resistor element connectors and the electrodes are covered with an electric conductor.
The electric conductor serves as a connector for the resistor element electrode, terminal(s) and the like and has a predetermined wiring pattern.
In a typical thin-film pressure sensor, a silicon oxide layer, polysilicon layer and aluminum layer are deposited on a surface of a diaphragm, an aluminum-layer pattern is formed by a photolithography etching, and the aluminum-layer pattern and the polysilicon layer are selectively removed by an etching to provide a pressure-sensitive-layer pattern and an electrode-wiring pattern (Patent Literature 1: JP-A-563-228764).
In another typical example (strain detection element), a thin-film resistor is formed on an insulation film of a straining portion using vapor-deposit, sputtering and the like and an electrode thin film is formed on the thin-film resistor using vapor-deposit, sputtering and the like (Patent Literature 2: JP-B-4452526).
In Patent Literatures 1 and 2, the pattern of the resistor element and conductor is formed using vapor-deposit and the like. However, when the pattern of the resistor element and the pattern of the conductor are misaligned with each other, the areas of the plurality of resistor elements exceed or fall short of a designed value.
When the areas of the resistor elements exceed or fall short of the designed value, the resistance of the resistor elements become different from a desired value, resulting in variation in the output of the resistor elements. The variation of the output of the resistor elements is unfavorable and thus an output adjustment of the resistor elements is required. However, the output adjustment requires complicated processes.
The problem associated with the typical examples will be described below with reference to schematic illustrations shown in FIGS. 8A to 8C.
FIG. 8A shows a detector 200A assumable based on Patent Literatures 1 and 2.
The detector 200A is provided on a flat portion of a diaphragm (not shown). The detector 200A includes four strain gauges 700.
The strain gauge 700 includes two central strain gauges 710, 720 and two outer strain gauges 730, 740. A resistor element connector 800 (a first resistor element connector 810, a second resistor element connector 820, a third resistor element connector 830 and a fourth resistor element connector 840) is connected to the strain gauge 700.
The first electrode 910 is connected to the first resistor element connector 810. The second electrode 920 is connected to second resistor element connector 820. The third electrode 930 is connected to the third resistor element connector 830. The fourth electrode 940 is connected to the fourth resistor element connector 840.
A part of the first resistor element connector 810 and the first electrode 910 are covered with a first electric conductor 1100. A part of the second resistor element connector 820 and the second electrode 920 are covered with a second electric conductor 1200. A part of the third resistor element connector 830 and the third electrode 930 are covered with the third electric conductor 1300. A part of the fourth resistor element connector 840 and the fourth electrode 940 are covered with a fourth electric conductor 1400.
The first electric conductor 1100 to the fourth electric conductor 1400 define an electric conductor 1000. Regions S1 to S4 are defined by a part of the strain gauge 700 and the resistor element connector 800 not covered with the electric conductor 1000.
When the electric conductor 1000 of the above detector 200A is vertically shifted with respect to the strain gauge 700 and the resistor element connector 800 as shown in FIG. 8B, or when the electric conductor 1000 of the above detector 200A is horizontally shifted with respect to the strain gauge 700 and the resistor element connector 800 as shown in FIG. 8C, the area of the regions S1 to S4 in FIG. 8B or 8C becomes different from the area of the regions S1 to S4 shown in FIG. 8A. Consequently, the outputs of the plurality of strain gauges varies.